High temperature gas turbine systems

ABSTRACT

High temperature gas turbine generation systems utilizing multiple heating stages between the primary compressor and expander, including coal based reactors and direct fired combustors.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to gas turbine generation systems, and moreparticularly provides systems utilizing multiple heating stagesincluding direct firing between the turbine compression and expansionstages.

2. Description of the Prior Art:

Present gas turbine technology can permit the use of relatively highturbine expander inlet temperatures, up to 1425° K. for base loadapplications. However, heat exchanger technology practically limits gasinlet temperatures to about 1075° K. Advanced designs have been proposedwhich could increase heat exchanger discharge temperatures to about1275° K., but which still would not match the gas turbine performancepotential.

To obtain higher expander inlet temperatures, components imparting heatto the expansion medium have been interposed between the compression andexpansion stages. For example, it is known to heat the compressedoxidant in a convective air heater and subsequently a coal firedatmospheric fluidized bed combustor, prior to entry into the expander.In such systems gaseous products discharged from the fluidized bedcombustor are directed to the convective air heater. Exhaust from theexpander is directed to the fluidized bed as a heating and fluidizinggas. While such systems increase the expander inlet temperature, theincrease does not take full advantage of the expander capability.

It is therefore desirable to provide gas turbine generation systemswhich allow utilization of the full capability of a modern gas turbineexpander.

SUMMARY OF THE INVENTION

This invention provides systems which allow for utilization of the fullthermal capability of existing gas turbine expanders by the directcombustion of a natural gas or petroleum distillate. The systems alsoprovide for utilization of existing fluidized bed gasifier or carbonizertechnology to generate clean fuel from coal or other hydrocarbonaceousmaterials, which is advantageously used to increase the temperature ofthe medium entering the expander. Additionally, the systems are readilycompatible not only with base-load operation, but also with load followoperational requirements, and are easily controllable during systemstartup and shutdown operations.

The systems heat and combust fuel, through several stages, indirectlyand directly with an oxidant, such as air, which flows between thecompressor discharge and the expander inlet. One of the stages is areactor which exothermically reacts coal or similar carbonaceousmaterials, and the compressed air flows, in heat exchange relation,through the reactor, absorbing heat. A portion of the thermal energy inat least one reactor is advantageously provided by the exhaust from theturbine expander. The air also flows to a direct combustor, where it isfired with a liquid or gaseous fuel and heated to a desired temperature,which can be up to 1425° K. The direct firing thus achieves temperaturesin the high temperature product gas of the combustion, compatible withturbine state-of-the-art material technology, thereby providingincreased overall system efficiency.

In a primary embodiment, air discharged from the compressor is conductedto and through a coal fired convective air heater. It then flows withinconduits through a fluidized bed heater, and to a supplementalcombustor. In the combustor it is reacted with a clean gaseous or liquidfuel. The air and fuel react in the combustor and are discharged to theturbine expander at the desired high temperature of approximately 1425°K. The exhaust from the expander is discharged to the fluidized bedreactor, where a portion of its thermal energy is recovered. The exhaustalso functions as a fluidizing medium. The fluidized bed heater may bereplaced by a pulverized coal fired combustor for heating the air.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, nature and additional features of the invention willbecome more apparent from the following description, taken in connectionwith the accompanying drawing, in which FIGS. 1 through 5 show alternateexhaust heated, supplemental fired, gas turbine system configurations inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 there is shown a high temperature gas turbinegeneration system including a compressor 110, expander 112, andelectrical generator 114. Mechanical rotational energy generated in theexpander 112 is transferred through a shaft 116 to the compressor 110,and through another shaft 118 to the generator 114. Reference numeralsused throughout this description all contain three digits. Common finaldigits among the numerals of the various figures refer to similarelements. For example, reference numerals 110, 210, and 310 identify acompressor, respectively, in FIGS. 1, 2, and 3.

An oxidant, such as oxygen or air, is fed through means for conductingthe oxidant, such as a conduit 120, to an inlet 122 of the compressor110. Typically, air enters the compressor at atmospheric temperature andpressure conditions. The air is compressed, and discharged fromcompressor 110 into conduit 113 at an increased pressure and temperaturethrough an outlet 124. Also shown is a conduit 133 through which a minorportion of the compressed air is directed from the compressor 110 to theexpander 112 through a heater exchanger 109 to provide cooling flow forthe expander vanes, blades and rotor.

Compressed air from the compressor 110 flows in series through a firstreactor or combustion heater 115, and a second reactor 117, prior todirect combustion in a supplemental combustor 134. Second reactor 117 ispreferably of the atmospheric fluidized bed type, reacting particulatecoal and sorbent entering through a conduit 158 with discharge gas fromthe expander 112 to produce a fuel gas discharged through a conduit 119.Spent sorbent and ash are removed through a conduit 121. The fuel gas isburned in the first reactor 115, of the combustion heating type.Reaction products are discharged through a conduit 123 and waste heat isrecovered in a waste heat boiler 125 which receives a condensate throughan inlet 127 and discharges process steam through an outlet 129. Aportion of the discharge gas from the expander 112 bypasses the reactors117, 115 through conduit 131, and heat therein is also recovered in thewaste heater boiler 125. The bypass is required to minimize the size andcost of the atmospheric fluidized combustion air heater. The fluidizedbed reactor 117 can also be replaced with a pulverized coal firedcombustor, for example a cyclone combustor with radiant heated air pipesin the wall.

Subsequent to the two stage exhaust fired heating through heat exchangeand reaction within the reactors 115, 117, the compressed air is reactedin the combustor 134 with a clean gaseous or liquid fuel, such asnatural gas provided from an independent fuel source 148.

Table I presents typical state points throughout the system of FIG. 1,lettered stations in Table I corresponding to the letter in FIG. 1.

    ______________________________________                                                PRESSURE   TEMPERATURE   REFERRED                                     STATION (kPa)      (°K.)  FLOW RATE                                    ______________________________________                                        A       101.4      288           1.000                                        B       1006.0     506           0.107                                        C       1006.0     597           0.893                                        D       990.8      703           0.893                                        E       976.3      1089          0.893                                        F       966.0      1367          0.899                                        G       110.3      811           1.006                                        H       110.3      811           0.771                                        I       110.3      811           0.235                                        J       105.2      1144          0.253                                        K       104.1      811           0.253                                        L       104.1      811           1.024                                        M       101.4      422           1.024                                        N       124.1      288           0.018                                        O       105.2      1144          0.009                                        P       1723.8     288           0.006                                        ______________________________________                                    

As shown from Table I, the high temperature gaseous product enters theexpander at 1425° K. Thus, direct combustion as disclosed provides atemperature increase at the expander inlet of approximately 300° K. withrespect to prior systems.

The supplemental combustor 134 can be readily adjusted to control thestate of the gaseous product entering the expander 112, advantageouslyallowing other than base load operation. Additionally, startup andshutdown operation is substantially simplified as compared to priorindirectly heated systems. Particularly for startup and shutdown, asecondary source of fuel gas or liquid can be provided to the combustor134, shown as conduit 144.

Reactor 117 contains a fluidized bed 152 of particulatehydrocarbonaceous material 154, such as coal, fluidized above a gridplate 156. The coal is fed to the reactor 117 through the conduit 158,and a sorbent, such as limestone, is fed to the reactor through the sameor a separate conduit. The discharge gas entering the reactor 117through the conduit 144 causes fluidization. Within the fluidized bed152, combustion and desulfurization take place.

FIG. 2 shows a system similar to FIG. 1 except that a portion of thecompressed air enters the combustor 234 after passing through the firstheater 215. The air is split at valve means 235 so that a portion passesthrough a conduit 237 to the combustor 234, and a second portion passesthrough conduit 239 to the second reactor 217. Similarly, the hightemperature gaseous product discharged from the combustor is mixed in ahousing 241 with air from the second reactor 217, and flows throughconduit 238 to the expander 212. This embodiment is particularlyadvantageous because it avoids the design of a combustor which willaccept 1075° K. combustion air.

FIG. 3 shows a system which is similar to that of FIG. 2, except that afirst portion of the compressed air directly from the compressor 310 isburned in the combustor 334, and a second portion of the air is placedin heat exchange relation with the two reactors 315, 317. The hightemperature combustion product gas from the combustor 334 is mixed in ahousing 341 with the heated second portion and then directed throughconduit 338 to the expander 312. This system is particularlyadvantageous because it permits the use of a conventional gas turbinecombustor which uses compressor discharge air at relatively lowtemperature as the oxidant.

An alternative system, where a fuel gas for the combustor is generatedfrom the oxidant heating apparatus, is shown in FIG. 4. Here, compressedoxidant from compressor 410 and heater 415 passes through a fluidizedbed reactor 417, similar to the system of FIG. 1. The reactor 417receives particulate coal through conduit 458, sorbent through a conduit459, recycled char through a conduit 474, and expander 412 dischargethrough a conduit 444. Within the fluidized bed combustion anddesulfurization take place, achieving temperatures in the range of 1025°to 1275° K., and discharging char and ash carried in a product gas ofcarbon dioxide, water vapor and nitrogen through a conduit 464 to acyclone 466. The waste combustion products are discharged from thecyclone 466 through a conduit 467. Waste heat in these products can berecovered in heat exchange apparatus, not shown. Char fines, sorbentfines and ash are discharged from the cyclone 466 through a conduit 468,and are selectively directed through valve means 472 and conduits 474,476 back to the reactor 417 and to a fluidized bed gasifier 478. Thebulk of the char fines enter reactor 478, and are fluidized above a gridplate 480. Steam and air are fed to the reactor 478, respectively,through conduits 482 and 484. Within the reactor 478 the char isgasified, discharging a raw fuel gas through a conduit 486 and waste ashthrough a bottom outlet 488. The fuel gas is preferably passed throughcleaning means such as particulate removal purification apparatus 490,where solid particulates are removed, and discharged directly or througha compressor 492 to the combustor 434.

Another manner in which the system can generate a clean fuel gas burningin a combustor 534 is shown in FIG. 5. Here, the reactor 417 of FIG. 4is replaced with a carbonizer 599. Particulate coal enters thecarbonizer 599 through a conduit 558, and heat, for example in the formof a hot gas, enters the carbonizer through a conduit 597. Thecarbonizer 599 generates a raw pyrolysis gas which is directed throughconduit 563 to conventional gas cleaning apparatus 595. The cleaned gasis then discharged through a conduit 593 to the combustor 534, to reactwith heated oxidant.

The disclosed systems are readily compatible with so-called combinedcycle power generation or cogeneration applications. A particularembodiment is shown in FIG. 6. Here, the combustion products aredirected to the expander 612 from any of the systems discussed above.Preferably, however, pulverized coal and preheated oxidant react in acombustion heater 617, and the products are directed through a cleaningapparatus to the expander 612. The discharge from an expander 612 isdirected through conduit 644 to a heat recovering steam generator 689. Aportion of the discharge can be directed through conduit 687 to provideheat to other subsystems, such as a process heat utilization system. Theprimary stream, however, enters the steam generator 689 and dischargesheat to a utilization fluid, such as water, to be transformed intosteam. The discharge from the expander 612 which enters the steamgenerator 689 is then discharged to a stack, or to another processsubsystem, through conduit 685. As shown, recycled condensate enters afeedwater heater 683 from a conduit 681, and is discharged into thecascading heating loops 679 and condensate pumps 677 of the steamgenerator 689. Steam which is generated is passed through conduit 675 toa steam turbine 673, which drives a generator 671. Discharge from thesteam turbine 673 is directed through conduits 669, 667 as processsteam. The process steam, subsequent to giving up a portion of itsenergy and condensation, is returned to the feedwater heater 683 throughconduit 681.

There have been described systems utilizing both directly and indirectlyfired combustion of compressed oxidant and other oxidant heating stagesfired in part by carbonaceous material clean fuel and turbine expanderdischarge. The systems all provide a high temperature combustion productto the turbine expander which allows for substantial increases inoverall system efficiency.

We claim:
 1. A high temperature gas turbine generation systemcomprising:a compressor; means for conducting a gaseous oxidant to saidcompressor; a combustion heater wherein one of a fuel gas and apulverized carbonaceous material is combusted to produce heat andreaction products; means for conducting compressed gaseous oxidant toand through said combustion heater so as to heat said oxidant; a reactorhousing a fluidized bed wherein particulate coal is reacted with adischarge gas to produce heat and said fuel gas; means for conductingsaid fuel gas from said reactor to said combustion heater; a combustorproducing a high temperature gaseous product from said heated oxidantand a gaseous fuel; means for conducting said gaseous fuel to saidcombustor; means for conducting a first portion of said heated oxidantto said combustor; means for conducting a second portion of said heatedoxidant to and through said reactor so as to further heat said secondportion of oxidant; means for mixing said high temperature gaseousproduct and said further heated second portion of oxidant into amixture; an expander having an inlet for receiving said mixture and anoutlet for discharging said discharge gas; means for conducting saidmixture to said expander inlet; and means for conducting said dischargegas from said expander outlet to said reactor.